Method of cleaning a surface region covered with contaminant or undesirable material

Abstract

The present invention relates to a method of cleaning a surface at least partly covered with contaminant or undesired material by applying atomic hydrogen. The invention also proposes an irradiation unit adapted to perform the cleaning method. In the present method the atomic hydrogen is generated by dissociation of molecular hydrogen directed to a surface containing catalytic material, which causes the dissociation of at least a part of the molecular hydrogen to atomic hydrogen. The surface with the catalytic material is arranged close to the surface to be cleaned and is dimensioned such that its total surface area is at least twice the surface area of the to be cleaned surface region. The method allows for the cleaning of the surface region in a constructive simple and efficient manner.

1. A method of cleaning a first surface region at least partly covered with contaminant or undesirable material, said contaminant or undesirable material being removable or convertible by exposure to atomic hydrogen, wherein the method includes:
 providing one or several second surface regions with catalytic material ( 11 ) in proximity to the first surface region,
 said catalytic material ( 11 ) being selected to cause dissociation of molecular hydrogen and 
 said one or several second surface regions having a total surface area which is at least twice a surface area of said first surface region, 
 
 directing a gas flow of a molecular hydrogen containing gas ( 8 ) or gas mixture to or along said one or several second surface regions in such a manner that
 said molecular hydrogen containing gas ( 8 ) or gas mixture gets in contact with said one or several second surface regions before passing said first surface region, wherein part of the molecular hydrogen dissociates to atomic hydrogen which is transported with said gas flow to the first surface region removing or converting said contaminant or undesirable material. 
 
 
     
     
       2. The method according to  claim 1 ,
 wherein said one or several second surface regions with catalytic material ( 11 ) are provided on one or several components ( 2 ,  3 ,  10 ) of a device, in which said first surface region is arranged, said components ( 2 ,  3 ,  10 ) apart from comprising the second surface regions also fulfilling other functions required for operation of said device. 
 
     
     
       3. The method according to  claim 1 ,
 wherein said first surface region is at least part of an optical surface of an optical component ( 3 ) in an irradiation unit for EUV-radiation and/or soft X-rays and said contaminant material is debris material deposited on said optical surface. 
 
     
     
       4. The method according to  claim 3 ,
 wherein said one or several second surface regions are surface regions of components ( 2 ,  3 ,  10 ) and/or of an inner wall of a vacuum vessel ( 2 ) of said irradiation unit and/or of instream positioned dedicated devices. 
 
     
     
       5. The method according to  claim 3 ,
 wherein said one or several second surface regions are surface regions of the optical surface and/or surface regions of backsides of optical components ( 3 ) of said irradiation unit. 
 
     
     
       6. The method according to  claim 3 ,
 wherein said optical component is a collector mirror ( 3 ) and at least a part of said one or several second surface regions is provided on front and/or backsides of shells of said collector mirror ( 3 ). 
 
     
     
       7. The method according to  claim 6 ,
 wherein said gas flow of a molecular hydrogen containing gas ( 8 ) or gas mixture is directed to the collector mirror ( 3 ) from a side opposite to a radiation source ( 1 ) of the irradiation unit towards the radiation source ( 1 ). 
 
     
     
       8. The method according to  claim 4 ,
 wherein said one or several second surface regions are provided inside one or several gas supplies ( 10 ) for supplying the molecular hydrogen containing gas ( 8 ) or gas mixture to the optical surface. 
 
     
     
       9. The method according to  claim 1 ,
 wherein said catalytic material ( 11 ) is selected from the materials Pd, Pt, Ru and Rh. 
 
     
     
       10. Irradiation unit, in particular for EUV-radiation and/or soft X-rays, comprising at least a radiation source ( 1 ) and one or several optical components ( 3 ) in a vacuum vessel ( 2 ) having one or several gas inlet ( 10 ) and gas outlet passages ( 9 ), wherein
 one or several surface regions with catalytic material ( 11 ) are arranged in proximity to at least one optical surface region of at least one of the optical components ( 3 ),
 said catalytic material ( 11 ) being selected to cause dissociation of molecular hydrogen and 
 said one or several surface regions with catalytic material ( 11 ) having a total surface area which is at least twice a surface area of said optical surface region, and 
 
 at least one of said one or several gas inlet passages ( 10 ) is formed to direct a gas flow along said one or several surface regions with catalytic material ( 11 ) in such a manner that said gas gets in contact with said one or several surface regions with catalytic material ( 11 ) before passing said optical surface region. 
 
     
     
       11. Irradiation unit according to  claim 10 ,
 wherein said one or several surface regions with catalytic material ( 11 ) are inner surface regions of the one or several inlet passages ( 10 ) and/or of an inner wall of the vacuum vessel ( 2 ) and/or of instream positioned dedicated devices. 
 
     
     
       12. Irradiation unit according to  claim 10 ,
 wherein said one or several surface regions with catalytic material ( 11 ) are surface regions of optical surfaces and/or of backsides of said one or several optical components ( 3 ). 
 
     
     
       13. Irradiation unit according to  claim 10 ,
 wherein one of said optical components is a collector mirror ( 3 ) and at least a part of said one or several second surface regions is provided on front and/or backsides of shells of said collector mirror ( 3 ). 
 
     
     
       14. Irradiation unit according to  claim 13 ,
 wherein said at least one of said one or several gas inlet passages ( 10 ) is arranged to direct the gas flow to the collector mirror ( 3 ) from a side opposite to the radiation source ( 1 ) towards the radiation source ( 1 ). 
 
     
     
       15. Irradiation unit according to  claim 10 ,
 wherein said catalytic material ( 11 ) is selected from the materials Pd, Pt, Ru and Rh.